Because 4,4'-dinitrodiphenylamine is easily reduced into 4,4'-diaminodiphenylamine, it is mainly used as a raw material for an antioxidant for a dye or rubber. Japanese Patent Publication No. Heisei 10-168038 (1998) describes a method for synthesizing diaminodiphenylamine such synthesizing method involving a reduction of dinitrodiphenylamine. In the above mentioned patent publication, a diaminodiphenylamine compound is described as being highly effective as an intermediate of an antioxidant or antiaging agent. 4,4'-diaminodiphenylamine or its derivatives, besides being used as an intermediate of an additive to rubber, are also used as an intermediate of dyes, agricultural chemicals and medical substances.
An example of conventional methods for preparing 4,4'-dinitrodiphenylamine involves nitration and deacetylation of N-acetyldiphenylamine. Such a method, however, is problematic in that the nitration is non-uniformly carried out. Furthermore, there is an inconvenience in that the nitrodiphenylamine inevitably produced is removed using a recrystalization from alcohol. With another method for preparing 4,4'-dinitrodiphenylamine, U.S. Pat. No. 4,990,673 (1991) discloses a method in which 4-chloroaniline is reacted with alkali metal cyanate to produce 4,4'-dinitrodiphenylamine. However, a disadvantage with this method is that the reaction must be carried out at a temperature of 160.degree. C. or above for an extended period of time of more than 15 hours.
In addition, another method of preparing the dinitrodiphenylamine derivative is the reaction of 4-nitroaniline with a nitrobenzene derivative (see, J. Am. Chem. Soc., 1976, (1), pp 138-143). Such a reference describes a method in which 4-nitroaniline and nitrobenzene derivatives are allowed to react using potassium t-butoxide (t-BuOK) as a base, thereby producing 2,4.sup.1 -dinitrodiphenylamine or 4,4'-dinitrodiphenylamine depending on the amount of the base, or alternatively producing 5-chloro (bromo)-2,4'-dinitrodiphenylamine using halogen as a substitute.
The present invention relates to a method of selectively preparing 4,4'-dinitrodiphenylamine using a nucleophilic aromatic substitution for hydrogen (hereinafter, called "NASH"). The NASH reaction recently proposed is advantageous in that, since amine or amide is reacted directly with nitrobenzene or its derivative in the presence of a base, any hazardous material or any intermediate, which is difficult to be removed, is not produced.
A process is also known wherein aniline and nitrobenzene are directly reacted in the presence of a base, such as "TMA(OH)", to prepare 4-nitrodiphenylamine (hereinafter, called "4-NDPA") and 4-nitrosodiphenylamine. See, J. Am. Chem. Soc., 1992, 114(23), 9237-8; U.S. Pat. No. 5,117,063; U.S. Pat. No.5,253,737; U.S. Pat. No. 5,331,099; U.S. Pat. No. 5,453,541; U.S. Pat. No. 5,552,531; and U.S. Pat. No. 5,633,407.
In addition, the use of the NASH reaction is described in U.S. Pat. No. 5,436,371, U.S. Pat. No. 5,117,063, and International Patent Publication No. WO 93/24447. These patents disclose a method of synthesizing N-(4-nitrophenyl)benzamide using benzamide rather than aniline. More concretely, prior art describes preparing 4-nitroaniline by synthesizing N-(4-nitrophenyl)benzamide using nitrobenzene in the amount of about 1 mole based on benzamide and then by hydrolyzing the resulting product with water or ammonia. However, there is no mention of the preparation of 4,4'-nitrodiphenylamine. This seems to be because N-(4-nitrophenyl)benzamide produced by a reaction of amide and nitrobenzene is a stable and separable compound, so that it is no longer reacted with nitrobenzene.